In the field of packaging of electronic components metallised (or conductive) foils have a wide application spectrum. They are used for a lot of different reasons such as for example gas or steam tightness, moisture protection, sterile packaging, UV light protection etc. and especially antistatic and electrical discharge protection as well as the attenuation of interfering fields from outside the bag. Such foils may reduce or prevent RFID communication through the foil.
RFID-communication works as follows: an electromagnetic field is sent from a transmitting antenna (RFID-reader) to a receiving antenna (RFID-tag). The received energy may be used for powering the RFID-tag and also for the transfer of information to the RFID-tag. The RFID-tag creates an answer which is a load modulation of the received electromagnetic field, which the RFID-reader detects. The electromagnetic field transmitted by the RFID-reader may create an eddy current in the electrically conductive layer of metallised or conductive foils. The eddy current may generate a reversed magnetic field or a reaction or reflected flux that is working against the electromagnetic field of the RFID-reader thereby reducing or prohibiting the communication through the foil. Another effect of a metallised or conductive foil on a RFID-communication is that
a) the RFID-tag does not receive any information because the electromagnetic field is absorbed by the foil and
b) the RFID-reader does not see any information as the foil produces a low-impedance or a permanent short circuit and therefore reduces the modulation depth of the signal.
Furthermore the RFID-tag or receiving antenna resonance frequency may be changed because of inductive and capacitive coupling effects of the electrically conductive layer of the foil. All these facts result in the following effects: the receive field and the receive distance of a RFID-communication system is reduced. The answer created by the RFID-tag is reduced so that more sensitive RFID-readers are needed.There is a rising need to equip electronic components with an RFID-tag carrying certain information about the component.
DE 10 2005 018 410 A1 discloses a packaging out of plastic, paper and/or cardboard with a coating containing metal pigments. The coating on the packaging is so thin that it is transmissive for electromagnetic radiation and RFID. According to this document the metallic coating is present for optical reasons.
DE 10 2004 040 831 A1 discloses a packaging for electronic components. The packaging according to the prior art comprises a carrier layer with an electrically conductive layer. The electrically conductive layer provides shielding characteristics to the packaging. The electrically conductive layer has a structure and/or a coating that reduces the shielding characteristic of the electrically conductive layer of the packaging in the area of the structure and/or coating. The structure is described in DE 10 2004 040 831 A1 as a “cut” that divides the electrically conductive plane of the electrically conductive layer into several electrically conductive planes. Relevant for the shielding characteristics of the known packaging are the shape and the dimension of those remaining electrically conductive planes. As examples for a certain shape are described an open and a closed circuit, whereby the shielding characteristics of the open circuit are not very high and the shielding characteristics of the closed circuit are very high. Furthermore, the shielding characteristics of bigger continuous conductive areas are supposed to be better than the shielding characteristics of smaller continuous conductive areas. When such a foil is used as a RFID-transmissive packaging for electronic components it is important to arrange the RFID-tag and the described structure and/or coating in a close relationship. Otherwise the shielding characteristics of the foil would prevent the RFID-communication through the foil.
There is the need to provide a material for packaging of electronic components that has RFID-transmissive characteristics and at the same time antistatic characteristics in a given area.